Browsing by Author "De Kwaadsteniet, Michele"

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    Characterization of an antimicrobial peptide from Enterococcus faecium active against bacteria associated with sexually transmitted diseases
    (Stellenbosch : Stellenbosch University, 2006-04) De Kwaadsteniet, Michele; Stellenbosch University. Faculty of Science. Department Microbiology.
    ENGLISH ABSTRACT : Urogenital tract infections are a major health problem among women. These infections include sexually transmitted diseases such as gonorrhoeae, chlamydia, syphilis and acquired immunity deficiency syndrome (AIDS) (Parratt and Hay, 2003), as well as opportunistic urogenital infections such as vaginosis and abnormal urinary tract infections (Foxman, 2003; Sobel and Chaim, 1996; Wang, 2000). Vaginosis and urinary tract infections affect more than 1 billion women worldwide annually (Reid and Bruce, 2003). Antibiotic resistance and the public demand for natural products have shifted the focus towards the application of probiotic lactic acid bacteria to try and combat these infections. Probiotics are marketed as microbial food supplements or capsules that may prevent diseases and clinical disorders (Schrezenmeir and de Vrese, 2001 ). Most of the well-known probiotics are lactic acid bacteria and include species such as Lactobacillus rhamnosus GR- 1 and Lactobacil/us fermentum RC-14 (Hoesl and Altwein, 2005; Stiles and Holfzapel, 1997). Many of these bacteria are natural inhabitants of the urogenital tract which they colonize to form a protective barrier against intestinal pathogens (Hoesl and Altwein, 2005; Song et al., 1999). Some probiotic strains produce antimicrobial peptides (bacteriocins ), usually with a narrow spectrum of activity, i.e. inhibition of only a certain group of pathogens (Klaenhammer, 1993). Bacteriocins are secreted either through ATP-binding cassettes (ABC) - transporters or via a general secretion pathway. Bacteriocins secreted by ABC-transporters have a doubleglycine- type leader sequence in their N-terminal, which serves as a recognition signal for protein procession and secretion (Haverstein et al., 1995). A sec-dependent leader signal peptide is characteristic of bacteriocins secreted through the general secretion pathway. The sec-dependent leader peptide is usually positively charged with a hydrophobic core and a specific cleavage region (von Heijne and Abrahmsen, 1989). In this study, lactic acid bacteria were screened for the production of bacteriocins active against uropathogenic strains of Enterococcus faecalis and Candida albicans. Enterococcus faecalis is usually associated with secondary bacteraemia of the urogenital tract and is linked to a large number of hospital-acquired infections. Human immunodefiency virus (HIV) patients are especially susceptible to E. faecalis infections. Candida albicans, on the other hand, is an opportunistic pathogen responsible for 80-90% of reported cases of candidal vaginosis, which is diagnosed in approximately 75% of women (Sobel, 1993). Approximate1y half of the patients suffering from candidal vulvovaginitis (CW) suffer from follow-up infections (Ferrer, 2000). Strain TB, isolated from vaginal secretions of children infected with HIV, inhibited the growth of uropathogenic strains of E. faeca/is and was identified as an Enterococcus faecium isolate. Two additional strains, Lactobacil/us plantarum 423 and Enterococcus mundtii ST15, isolated from sorghum beer and soy flour, respectively, also inhibited E. faecalis and were included in the study. None of the three strains produced hydrogen peroxide. All three strains produced bacteriocin-like peptides that inhibited E. faecalis. Plantaricin 423, produced by L. plantarum 423, has been described previously (van Reenen et al., 199B) and is similar to pentocin TV35b (Okkers et al., 1999). Bacteriocin ST15, produced by Enterococcus mundtii ST15, is similar to mundticiin ST 4SA produced by a different strain of E. mundtii (Knoetze, Department of Microbiology, University of Stellenbosch, personal communication). Bacteriocin TB, produced by E. faecium TB, is a class I la sec-dependent bacteriocin and may be considered a novel peptide produced by enterococci. The operon containing the structural gene, a potential immunity gene and mobilization genes is located on a 7 kb-plasmid. The operon was sequenced and the mode of activity of bacteriocin TB determined. Bacteriocin TB is 69% homologous to bacteriocin 31, produced by Enterococcus faecalis Y1717 (Tomita et al., 1996). The signal peptide of bacteriocin TB is only 27% homologous to the signal peptide of bacteriocin 31. The immunity peptide of bacteriocin TB displayed 50% homology to that of bacteriocin 31.
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    Characterization of nisin F and its role in the control of respiratory tract and skin infections
    (Stellenbosch : University of Stellenbosch, 2009-03) De Kwaadsteniet, Michele; Dicks, Leon Milner Theodore; University of Stellenbosch. Faculty of Science. Dept. of Microbiology.
    Multidrug resistant strains of Staphylococcus aureus is presenting an increasing threat, especially immune compromised individuals. Many of these strains have developed resistance to newly approved drugs such as quinupristin-dalfopristin, linezolid and daptomycin. The search for alternative treatment, including bacteriocins (ribosomally synthesized antimicrobial peptides) of lactic acid bacteria is increasing . Lactococcus lactis subsp. lactis F10, isolated from freshwater catfish, produced a new nisin variant active against clinical strains of S. aureus. The operon encoding nisin F is located on a plasmid and the structural gene has been sequenced. The lantibiotic is closely related to nisin Z, except at position 30 where valine replaced isoleucine. The antimicrobial activity of nisin F against S. aureus was tested in the respiratory tract of Wistar rats. Non-immunosuppressed and immunosuppressed rats were intranasally infected with S. aureus K and then treated with either nisin F or sterile physiological saline. Nisin F protected immunosuppressed rats against S. aureus, as symptoms of an infection were only detected in the trachea and lungs of immunosuppressed rats treated with saline. The safety of intranasally administered nisin F was also evaluated and proved to have no adverse side effects. The potential of nisin F as an antimicrobial agent to treat subcutaneous skin infections was evaluated by infecting C57BL/6 mice with a bioluminescent strain of S. aureus (Xen 36). Immunosuppressed mice were treated with either nisin F or sterile physiological saline 24 h and 48 h after infection with subcutaneously injected S. aureus Xen 36. Histology and bioluminescence flux measurements revealed that nisin F was ineffective in the treatment of deep dermal staphylococcal infections. Non-infected and infected mice treated with nisin F had an influx of polymorphonuclear cells in the deep stroma of the skin tissue. This suggested that nisin F, when injected subcutaneously, may have modulated the immune system. Nisin F proved an effective antimicrobial agent against S. aureus-related infections in the respiratory tract, but not against subcutaneous infections. The outcome of nisin F treatment thus depends on the route of administration and site of infection.